The present invention relates to a device for transferring a fiber web, particularly a paper web, from the press section into the dry end of a paper manufacturing machine. The invention proceeds from a device in accordance with Federal Republic of Germany Patent 35 44 541, which corresponds to U.S. Pat. No. 4,768,294.
In this known device, the web travels in direct contact with the smooth shell of a press roll. Downstream of the press nip, the web continues its travel in contact with the shell of the press roll up to a place where the web detaches from the roll. There it is transferred onto a porous transport belt which travels over a guide roll arranged close to the press roll and over a drying cylinder which is arranged within the loop of the transport belt. The support belt of the following first dryer group is tangent to the circumference of the aforementioned drying cylinder and takes over the further transport of the web.
It is known to provide a first drive for the press roll, a second drive for the transport belt, and a third drive for the first dryer group. The speeds of these drives are controlled independently of one another. A positive speed differential of the second drive as compared with the first drive and also of the third drive with respect to the second drive can be established so that controllable elongation of the web takes place at both points of transfer.
One disadvantage of the known device is that the web must pass over a relatively long unsupported free path or open draw between the smooth press roll and the porous transport belt. There is thus the danger that the web, which is still moist, may travel unevenly at this place. In particular, the edges of the web tend to flutter. This can result in tearing of the web, although, as stated above, the web is stretched relatively little at this place. Another disadvantage is that the first drying cylinder is arranged within the loop of the transport belt so that the web does not come into contact with this cylinder. Substantial heating of the web therefore commences only at the second drying cylinder of the upper row of cylinders. Therefore, this known construction has not been introduced into actual practice.
In customary arrangements, there is no transport belt between the press section and the dry end. Therefore, the support belt of the first dryer group is brought by means of a guide roll, which may be a suction roll, as close as possible to the shell of the smooth press roll, as shown in Federal Republic of Germany Patent 33 44 217, which is equivalent to U.S. Pat. No. 4,677,763. The paper web travels from the smooth press roll over a relatively short free path of travel or open draw directly to the support belt. As an alternative, a paper guide roll is provided between the smooth press roll and the support belt if the smooth press roll does not come into contact with the bottom side of the web but instead contacts its top side.
These known arrangements have proven satisfactory in practice. However, difficulties have recently been encountered in increasing the operating speed of such a paper manufacturing machine to the desired extent and at the same time to sufficiently tension the paper web upon its introduction into the dry end. This initial tensioning is effected, as is known, by establishing a speed difference between the first dryer group and the smooth press roll. It has been found that establishing a relatively great difference in speed makes it necessary to provide a relatively great distance between the smooth press roll and the support belt. However, the danger of the fluttering of the edges of the web arises again. On the other hand, if that distance is made relatively small, to avoid the fluttering of the edges of the web, only a relatively small difference in speed can be established or else the paper web must be stretched strongly over a short distance, which may lead to tears in the web even in the event of only the slightest defects in the paper.